5 files changed, 92 insertions, 25 deletions
diff --git a/third_party/nix/src/libstore/rpc-store.cc b/third_party/nix/src/libstore/rpc-store.cc
index 2d1278f40c..f3fc5582f3 100644
--- a/third_party/nix/src/libstore/rpc-store.cc
+++ b/third_party/nix/src/libstore/rpc-store.cc
@@ -3,6 +3,7 @@
 #include <algorithm>
 #include <filesystem>
 #include <memory>
+#include <optional>
 
 #include <absl/status/status.h>
 #include <absl/strings/str_cat.h>
@@ -326,8 +327,32 @@ absl::Status RpcStore::buildPaths(const PathSet& paths, BuildMode buildMode) {
 
   google::protobuf::Empty response;
   request.set_mode(nix::BuildModeToProto(buildMode));
-  return nix::util::proto::GRPCStatusToAbsl(
-      stub_->BuildPaths(&ctx, request, &response));
+
+  // TODO(tazjin): Temporary no-op sink used to discard build output,
+  // but satisfy the compiler. A real one is needed.
+  //
+  // Maybe this should just be stderr, considering that this is the
+  // *client*, but I'm not sure.
+  std::ostream discard_logs = DiscardLogsSink();
+
+  std::unique_ptr<grpc::ClientReader<proto::BuildEvent>> reader =
+      stub_->BuildPaths(&ctx, request);
+
+  proto::BuildEvent event;
+  while (reader->Read(&event)) {
+    if (event.has_build_log()) {
+      // TODO(tazjin): Include .path()?
+      discard_logs << event.build_log().line();
+    } else {
+      discard_logs << std::endl
+                   << "Building path: " << event.building_path().path()
+                   << std::endl;
+    }
+
+    // has_result() is not in use in this call (for now)
+  }
+
+  return nix::util::proto::GRPCStatusToAbsl(reader->Finish());
 }
 
 BuildResult RpcStore::buildDerivation(const Path& drvPath,
@@ -339,11 +364,25 @@ BuildResult RpcStore::buildDerivation(const Path& drvPath,
   auto proto_drv = drv.to_proto();
   request.set_allocated_derivation(&proto_drv);
   request.set_build_mode(BuildModeToProto(buildMode));
-  proto::BuildDerivationResponse response;
-  SuccessOrThrow(stub_->BuildDerivation(&ctx, request, &response),
-                 __FUNCTION__);
 
-  const auto result = BuildResult::FromProto(response);
+  // Same note as in ::buildPaths ...
+  std::ostream discard_logs = DiscardLogsSink();
+
+  std::unique_ptr<grpc::ClientReader<proto::BuildEvent>> reader =
+      stub_->BuildDerivation(&ctx, request);
+
+  std::optional<BuildResult> result;
+
+  proto::BuildEvent event;
+  while (reader->Read(&event)) {
+    if (event.has_build_log()) {
+      discard_logs << event.build_log().line();
+    } else if (event.has_result()) {
+      result = BuildResult::FromProto(event.result());
+    }
+  }
+  SuccessOrThrow(reader->Finish(), __FUNCTION__);
+
   if (!result.has_value()) {
     throw Error("Invalid response from daemon for buildDerivation");
   }
diff --git a/third_party/nix/src/libstore/store-api.cc b/third_party/nix/src/libstore/store-api.cc
index 3ada63532c..7972f50836 100644
--- a/third_party/nix/src/libstore/store-api.cc
+++ b/third_party/nix/src/libstore/store-api.cc
@@ -92,7 +92,7 @@ nix::proto::BuildStatus BuildResult::status_to_proto() {
 }
 
 std::optional<BuildResult> BuildResult::FromProto(
-    const nix::proto::BuildDerivationResponse& resp) {
+    const nix::proto::BuildResult& resp) {
   BuildResult result;
   switch (resp.status()) {
     case proto::BuildStatus::Built:
@@ -125,7 +125,7 @@ std::optional<BuildResult> BuildResult::FromProto(
       return {};
   }
 
-  result.errorMsg = resp.error_message();
+  result.errorMsg = resp.msg();
   return result;
 }
 
diff --git a/third_party/nix/src/libstore/store-api.hh b/third_party/nix/src/libstore/store-api.hh
index 39769dfb3c..1d81b228f2 100644
--- a/third_party/nix/src/libstore/store-api.hh
+++ b/third_party/nix/src/libstore/store-api.hh
@@ -189,7 +189,7 @@ struct ValidPathInfo {
   virtual ~ValidPathInfo() {}
 };
 
-typedef std::list<ValidPathInfo> ValidPathInfos;
+using ValidPathInfos = std::list<ValidPathInfo>;
 
 enum BuildMode { bmNormal, bmRepair, bmCheck };
 
@@ -243,7 +243,7 @@ struct BuildResult {
   nix::proto::BuildStatus status_to_proto();
 
   static std::optional<BuildResult> FromProto(
-      const nix::proto::BuildDerivationResponse& resp);
+      const nix::proto::BuildResult& resp);
 };
 
 class Store : public std::enable_shared_from_this<Store>, public Config {
diff --git a/third_party/nix/src/nix-daemon/nix-daemon-proto.cc b/third_party/nix/src/nix-daemon/nix-daemon-proto.cc
index ec8e0ff42c..b7d5836091 100644
--- a/third_party/nix/src/nix-daemon/nix-daemon-proto.cc
+++ b/third_party/nix/src/nix-daemon/nix-daemon-proto.cc
@@ -29,7 +29,6 @@ namespace nix::daemon {
 
 using ::google::protobuf::util::TimeUtil;
 using ::grpc::Status;
-using ::nix::proto::BuildStatus;
 using ::nix::proto::PathInfo;
 using ::nix::proto::StorePath;
 using ::nix::proto::StorePaths;
@@ -271,9 +270,9 @@ class WorkerServiceImpl final : public WorkerService::Service {
         __FUNCTION__);
   }
 
-  Status BuildPaths(grpc::ServerContext*,
-                    const nix::proto::BuildPathsRequest* request,
-                    google::protobuf::Empty*) override {
+  Status BuildPaths(
+      grpc::ServerContext*, const nix::proto::BuildPathsRequest* request,
+      grpc::ServerWriter<nix::proto::BuildEvent>* /* writer */) override {
     return HandleExceptions(
         [&]() -> Status {
           PathSet drvs;
@@ -612,7 +611,7 @@ class WorkerServiceImpl final : public WorkerService::Service {
   Status BuildDerivation(
       grpc::ServerContext* context,
       const nix::proto::BuildDerivationRequest* request,
-      nix::proto::BuildDerivationResponse* response) override {
+      grpc::ServerWriter<nix::proto::BuildEvent>* writer) override {
     return HandleExceptions(
         [&]() -> Status {
           auto drv_path = request->drv_path().path();
@@ -625,11 +624,19 @@ class WorkerServiceImpl final : public WorkerService::Service {
             return Status(grpc::StatusCode::INTERNAL, "Invalid build mode");
           }
 
-          auto res = store_->buildDerivation(drv_path, drv, *build_mode);
+          BuildResult res = store_->buildDerivation(drv_path, drv, *build_mode);
+
+          proto::BuildResult proto_res{};
+          proto_res.set_status(res.status_to_proto());
+
+          if (!res.errorMsg.empty()) {
+            proto_res.set_msg(res.errorMsg);
+          }
 
-          response->set_status(res.status_to_proto());
-          response->set_error_message(res.errorMsg);
+          proto::BuildEvent event{};
+          *event.mutable_result() = proto_res;
 
+          writer->Write(event);
           return Status::OK;
         },
         __FUNCTION__);
diff --git a/third_party/nix/src/proto/worker.proto b/third_party/nix/src/proto/worker.proto
index fe89b292a2..6a80b3e32b 100644
--- a/third_party/nix/src/proto/worker.proto
+++ b/third_party/nix/src/proto/worker.proto
@@ -27,7 +27,7 @@ service WorkerService {
 
   // Build the specified derivations in one of the specified build
   // modes, defaulting to a normal build.
-  rpc BuildPaths(BuildPathsRequest) returns (google.protobuf.Empty);
+  rpc BuildPaths(BuildPathsRequest) returns (stream BuildEvent);
 
   // TODO: What does this do?
   rpc EnsurePath(StorePath) returns (google.protobuf.Empty);
@@ -90,7 +90,7 @@ service WorkerService {
 
   // Build a single non-materialized derivation (i.e. not from an
   // on-disk .drv file).
-  rpc BuildDerivation(BuildDerivationRequest) returns (BuildDerivationResponse);
+  rpc BuildDerivation(BuildDerivationRequest) returns (stream BuildEvent);
 
   // Add signatures to the specified store path. The signatures are not
   // verified.
@@ -174,6 +174,32 @@ message Signatures {
   repeated string sigs = 1;
 }
 
+// Represents the outcome of a build for a single store path.
+message BuildResult {
+  StorePath path = 1;
+  BuildStatus status = 2;
+  string msg = 3;
+}
+
+// Represents an event occuring during a build.
+message BuildEvent {
+  message LogLine {
+    string line = 1;
+    StorePath path = 2;
+  }
+
+  oneof result_type {
+    // Build for a store path has finished
+    BuildResult result = 1;
+
+    // A line of build log output was produced
+    LogLine build_log = 2;
+
+    // Build for a store path has started
+    StorePath building_path = 3;
+  }
+}
+
 message IsValidPathResponse {
   bool is_valid = 1;
 }
@@ -316,11 +342,6 @@ message BuildDerivationRequest {
   BuildMode build_mode = 3;
 }
 
-message BuildDerivationResponse {
-  BuildStatus status = 1;
-  string error_message = 2;
-}
-
 message AddSignaturesRequest {
   StorePath path = 1;
   Signatures sigs = 2;